Lantibiotics are bactericidal peptides that contain the rare amino acids lanthionine and/or 3-methyllanthionine. Lantibiotics are produced by gram-positive bacteria and are derived from ribosomally-synthesized prepeptides. The prepeptides typically consist of an N-terminal leader sequence, which is cleaved off during or after secretion from the cell, and the C-terminal propeptide, which is post-translationally modified to form the mature lantibiotic (Jung (1991) Angewandte Chemie 30(9):1051–1192). One such post-translational modification comprises the enzymatic dehydration of serine or threonine residues to yield dehydroalanine (Dha) or dehydrobutyrine (Dhb), respectively (Weil, et al. (1990) Eur. J. Biochem. 194:217–223). Subsequently, SH-groups of the cysteine residues react with the double-bonds of Dha or Dhb residues to form lanthionine or methyllanthionine, respectively.
Lantibiotics are structurally and functionally diverse molecules. They range from elongated, cationic peptides of 34 amino acid residues in length to short, 19 amino acid, globular molecules with a net negative charge. Based on their structural and functional properties, the mature peptides have been subdivided into two groups, Type-A and Type-B (Jung (1991) supra). Type-A lantibiotics are elongated amphiphilic peptides that form transient pores in the membranes of sensitive bacteria (Sahl (1991) In G. Jung and H.-G. Sahl (ed.), Nisin and novel lantibiotics (p. 347–358) Escom, Leiden). Type-B lantibiotics are globular peptides produced by Streptomyces. They have molecular masses less than 2100 Da, share a high degree of amino acid sequence homology and have similar ring structures comprised of a head-to-tail condensation (Jung (1991), supra).
The Type-A class has been further divided into subgroups according to their propeptide sequences (Sahl and Bierbaum (1998) Annu. Rev. Microbiol. 52:41–79). Subgroup AI contains the nisin-like lantibiotics such as nisin, subtilin, epidermin and pep5 as the most thoroughly characterized members (Allgaier, et al. (1986) Eur. J. Biochem. 160:9–22; Gross, et al. (1968) FEBS Lett 2:61–64; Gross, et al. (1971) J Am. Chem. Soc. 93:4634–4635; Kaletta, et al. (1989) Arch. Microbiol. 152:16–19; Weil, et al. (1990) Eur. J. Biochem. 194:217–223). Subgroup AII consists of lacticin 481, SA-FF22, salivaricin and variacin (Hynes, et al. (1993) Appl. Environ. Microbiol. 59:1969–1971; Piard, et al. (1993) J. Biol. Chem. 268:16361–16368; Pridmore, et al. (1996) Appl. Environ, Microbiol. 62:1799–1802; Ross, et al. (1993) Appl. Environ. Microbiol. 59:2014–2021).
Another characteristic feature of lantibiotics is the prepeptide leader sequence, which is unrelated to the more common signal sequences utilized in sec-dependent transport systems. The leader peptides may play an important role in maturation of the lantibiotic through interactions with the modifying enzymes and transport system as well as the propeptide. Therefore, individual specificities may exist between the components of the modification system and the corresponding prepeptides upon which they operate. Grouping and classifying lantibiotics based on the leader peptide sequence is consistent with the classifications describe above (Sahl and Bierbaum (1998) supra).
The genes responsible for the biosynthesis of the lantibiotics are organized in operon-like structures. The biosynthetic locus of all members in subgroup AI comprises lanA, the structural gene for the lantibiotic; lanB and lanC, which encode the post-translational modifying enzymes of the preprolantibiotic; lanP, which encodes the processing protease; and lanT, which encodes the ABC transporter for secretion of the lantibiotic. Epidermin and gallidermin have an additional gene, lanD, which is responsible for C-terminal oxidative decarboxylation (Kupke, et al. (1994) J. Biol. Chem. 269:5653–5659; Kupke, et al. (1995) J. Biol. Chem. 270:11282–89).
In comparison, subgroup AII lantibiotics have simple biosynthetic loci. They are comprised of lanB and lanC, which are combined into one gene; lanM; and lanP and lanT, which are combined into lanT. (Chen, et al. (1999) Appl. Environ. Microbiol. 65:1356–1360; Qi, et al. (1999) Appl. Environ. Microbiol 65:652–658; Rince, et al. (1994) Appl. Environ. Microbiol. 60:1652–1657). Lantibiotic loci also contain a set of immunity genes, which are responsible for self-protection of the producing strains (Saris, et al. (1996) Antonie van Leewenhoek 69:151–159). Moreover, the expression of the lantibiotic genes is usually regulated either by a single transcriptional regulator (Peschel, et al. (1993) Mol. Microbiol. 9:31–39; Qi, et al. (1999) supra) or by a two-component signal transduction system (de Ruyter, et al. (1996) J. Bacteriol. 178:3434–3439; Klein, et al. (1993) Appl. Environ Microbiol. 59:296–303; Kuipers, et al. (1995) J. Biol. Chem. 270:27295–27304).
The lantibiotic duramycin, also known as PA48009 (FIG. 1), was isolated from the culture supernatant of Streptoverticillium cinnamoneum forma azacoluta (ATCC 12686; now referred to as Streptomyces cinnamoneus subsp. cinnamoneus) (Hayashi, et al., (1990) J. Antibiotics 43:1421; Pridham, et al. (1956) Phytopathology 46:575–581; Shotwell, et al. (1958) J. Am. Chem. Soc. 80:3912; Nakamura, et al. (1984) Biochem. 23:385). Duramycin contains a lysinoalanine, head-to-tail cross-bridge and a hydroxylated aspartic acid. Lysinoalanine results from an analogous reaction of the epsilon-NH2 group of lysine with dehydrolalanine. The ability of duramycin to increase chloride secretion has been reported (Stone, et al. (1984) J. Biol. Chem. 259: 2701; Cloutier, et al. (1987) Pediatr. Pulmonol. 1(Suppl): 112; Cloutier, et al. (1988) Pediatr. Pulmonol. 2(Suppl):99; Cloutier, et al. (1989) Pediatr. Pulmonol. 4(Suppl):116; Cloutier, et al. (1990) Am. J. Physiol. 259:C450). The use of duramycin for facilitating the removal of retained pulmonary mucus secretions has been provided (e.g., U.S. Pat. Nos. 5,849,706 and 5,716,931). Furthermore, duramycin inhibits the growth of B. subtilis by binding to phosphatidylethanolamine.